1. Field of the Invention
The present invention relates to an optical gauging apparatus utilizing the light reflected on an object to be gauged and being useful for gauging of, for example, car level, spring deflection and photographic distance.
2. Background Art
There have already been proposed various gauging apparatuses utilizing the light reflected on an object to be gauged, an example of which is schematically shown by FIG. 15 of the accompanying drawing.
This example of prior art includes a pair of point light sources 11, 12 used to illuminate an object 13 to be gauged.
The light reflected on the object 13 is incident on a light receiver 14 adapted to be exposed alternately to one light component emitted from the one light source 11 and then reflected on the object 13, on one hand, and another light component emitted from the other light source 12 and then reflected on the object 13, on the other hand. The light receiver 14 generates photoelectric conversion signals Sp, Ss corresponding to quantities of the reflected light components derived from the respective light sources 11, 12 and then received by this light receiver 14.
With such optical gauging apparatus of well known art, the object 13 has two different luminances Ep, Es based on the light components projected from the respective light sources 11, 12, because of a differential optical path length as shown in FIG. 16. Thus, surface luminances (nits) on the object 13 correspond to KEp and KEs, respectively, where K represents a reflection factor of the object 13. Accordingly, ratio of these surface luminances is expressed as follows: EQU Ep/Es .varies. Sp/Ss (1)
Therefore, a distance D to the object 13 can be determined by processing the photoelectric conversion signals Sp, Ss as functions of the distance.
The above-mentioned optical gauging apparatus of prior art is very advantageous in that the distance can be determined from the ratio of the surface luminances on the object 13 regardless the reflection factor K of the object 13, as will be apparently understood from said equation (1).
However, this apparatus of prior art uses a pair of light sources 11, 12 and will encounter a problem when intensities of the light components projected from these light sources 11, 12 vary at different rates, respectively, due to various causes such as deterioration thereof.
No problem occurs so far as the intensities of the light components projected from these light sources 11, 12 vary at a same rate, but variation of said intensities occurring at different rates will cause a false result of gauging.